This invention relates to a voltage regulator suitable for use with a generator such as an alternator, and in particular to a voltage regulator that provides improved control functions.
FIG. 9 shows a prior-art dual voltage alternator A that supplies output currents to two separate buses, a 28 volt bus and a 14 volt bus in this example. This alternator is suitable for use in a dual battery system that uses a first battery B1 interposed between ground and the 14 volt bus and a second battery B2 interposed between the 14 volt bus and the 28 volt bus.
In the conventional manner, the alternator A includes a field coil F and two sets of stator windings W. The stator windings W are connected by rectifying diodes D to the 28 volt bus, and the stator windings W are also connected to the 14 volt bus by winding switches such as SCR's S. Conventionally, the alternator A is controlled by a voltage regulator (not shown in FIG. 9) that controls current through the field coil F to regulate voltage on the 28 volt bus, and that controls the winding switches S to regulate voltage on the 14 volt bus.
In the past, voltage regulators have been constructed both as analog and as digital circuits, in some cases including microcomputers. See, for example, Kissel, U.S. Pat. No. 4,659,977, and Judge, U.S. Pat. No. 5,216,350. Falater, U.S. Pat. No. 5,225,764 discloses a digital voltage regulator that employs a duty cycle generator to vary the duty cycle of a field coil switch.
In spite of this work, a need presently exists for an improved voltage regulator that is both effective in operation and inexpensive in construction.